Issue 25, 2024

Light-induced spin-state switching in Fe(ii) spin-crossover complexes with thiazole-based chelating ligands

Abstract

Homoleptic complexes [Fe(4bt)3](ClO4)2 (1), [Fe(2bt)3](ClO4)2 (2), and [Fe(3tpH)3](ClO4)2 (3) were obtained by a reaction between the Fe(II) precursor salt and the corresponding thiazole-based bidentate ligand (L = 4bt = 4,4′-bithiazole, 2bt = 2,2′-bithiazole, 3tpH = 3-(thiazol-2-yl)pyrazole). X-ray crystal structure determination revealed crystallization of solvent-free complex 1, a solvate 2·MeOH, and a co-crystal 3·2(3tpH). The crystal packing of all these complexes is dominated by one-dimensional interactions between the [Fe(L)3]2+ cations. These interactions are stronger in 2·MeOH and 3·2(3tpH), leading to cooperative and slightly hysteretic transitions between the high-spin and low-spin electronic configurations at ∼235 K and 159 K, respectively. In contrast, weaker intermolecular interactions in 1 result in a gradual spin crossover above 300 K, with the maximum fraction of the HS state ∼25% achieved at 400 K. Complexes 2 and 3·2(3tpH) exhibit light-induced excited spin state trapping (LIESST) under irradiation with white light or a 532 nm laser at 5 K. After the photoexcitation, the trapped metastable HS state relaxes to the ground LS state with the average relaxation temperature of 81 K and 68 K, respectively. Examination of the relaxation dynamics by optical absorption spectroscopy on a single crystal of 3·2(3tpH) revealed the sigmoidal shape of the relaxation curves at lower temperatures, attributed to cooperative effects, as well as a plateau at ∼10% of the HS fraction at intermediate temperatures, hinting at a more complex mechanism for the relaxation of the LIESST phase in this material.

Graphical abstract: Light-induced spin-state switching in Fe(ii) spin-crossover complexes with thiazole-based chelating ligands

Supplementary files

Article information

Article type
Paper
Submitted
01 Febr. 2024
Accepted
28 Maijs 2024
First published
29 Maijs 2024
This article is Open Access
Creative Commons BY-NC license

Dalton Trans., 2024,53, 10511-10520

Light-induced spin-state switching in Fe(II) spin-crossover complexes with thiazole-based chelating ligands

M. Jo, B. Amanyazova, S. Yergeshbayeva, M. Gakiya-Teruya, Ö. Üngör, P. Lopez Rivera, N. Jen, E. Lukyanenko, A. V. Kurkin, R. Erkasov, M. W. Meisel, A. Hauser, P. Chakraborty and M. Shatruk, Dalton Trans., 2024, 53, 10511 DOI: 10.1039/D4DT00308J

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